The town of Cleanville lies next to a lake, which the residents of the town use for fishing, boating, and other recreational activities. Last year, two firms, Filth Inc. and Sludge Inc., built factories on the other side of the lake and have been dumping trash into it. Although some of the trash will dissipate naturally, the amount of trash the two firms emit is too much for the lake to handle. Right now, each firm dumps 40 pounds of trash in the lake each year (total of 80 pounds). Environmental scientists in Cleanville estimate that the lake can handle only 30 pounds of trash per year. The table below reports the marginal costs to the two firms of reducing trash.